1. Field of the Invention
The present invention relates to devices for detecting when objects such as equipment, articles of manufacture, or shipping containers have been subjected to a mechanical shock.
2. Description of the Prior Art
Many items of manufacture are sensitive to excessive force or shock, and may be damaged if subject to such force or shock. For example, electronic equipment such as televisions and stereos have plastic cabinets and sensitive electronic components. Excessive shock can result in breakage of the cabinet and electronic components.
These items of manufacture are particularly vulnerable to excessive forces when being shipped. For example, when loading or unloading shipping containers, the containers may be dropped from a forklift. Also, when being shipped in a railcar, the railcar may be stopped suddenly, exposing the shipping containers loaded inside to excessive acceleration forces. There is a need for a low cost, reliable device that can be attached to a shipping container and that will provide an indication if the container has been subjected to excessive forces. With such a device, a manufacturer can accurately access fault for damage caused to its goods in transit.
The prior art has seen development of many complex electrical, mechanical and electromechanical devices which measure force applied to a container or object. These devices have tended to be expensive to manufacture, restricting the extensive use of the devices on inexpensive as well as expensive objects
A simpler force sensor device is shown in Manske, U.S. Pat. No. 4,793,717. The Manske device can register the impact of a single direct impact. However, it apparently is not sensitive to a distributed surface of pressure such as a box surface. Additionally, the threshold of force needed to activate the Manske device is fixed by its design. Some applications may require different activating forces. For example, sensor devices used on televisions may require a relatively low activating force as compared to sensor devices on more robust equipment. Thus, it is desirable to provide a sensor device that can be manufactured in different sensitivities.